A radioactive decay rate of a radioactive element is found to be 1000 disintegrations per second at a certain time. If the half-life of the element is 1 second, the decay rate after one second is _ and after three seconds is _.
Correct answer: A. 500, 125
- A. 500, 125
- B. 1000, 1000
- C. 125, 500
- D. 100, 10
Explanation
The decay of a radioactive substance follows an exponential decay law. The rate of decay at any given time is proportional to the amount of the substance present. The half-life is the time it takes for half of the radioactive substance to decay.Initial decay rate: 1000 disintegrations per second (at t = 0 seconds)After 1 second:Since the half-life is 1 second, after 1 second, half of the radioactive material will have decayed. So, the remaining decay rate will be 500 disintegrations per second (half of the initial rate).After 3 seconds:At this point, the original radioactive substance has decayed to a quarter of its initial amount (2 half-lives). Therefore, the remaining decay rate will be 125 disintegrations per second.Comparing the decay rates:After 1 second: 500 disintegrations per secondAfter 3 seconds: 125 disintegrations per secondThe answer that matches this pattern is A: 500, 125.
Last updated
About Nuclear Physics
Atomic nuclei contain protons and neutrons, with nuclear size, mass defect and binding energy describing their stability. The work covers alpha, beta and gamma decay, decay equations, half-life and decay rate, along with radiation safety and medical applications such as imaging, radiotherapy and tracers.
Practise Nuclear Physics
1,254 free Nuclear Physics MCQs from Physics, each with the correct answer and an explanation. Unlimited attempts, no account needed.
Exams that ask Physics questions like this
Physics is on 13 papers prepared for on TestUstad, and all of them draw the same bank, so this question is worth knowing for every one of them.